A Whole Hole of Holes

If you're in a hole, the saying goes, stop digging. Nature evidently has ignored this advice - the image above shows a "hole" in the Milky Way which is filled with black holes. This hole, a sightline along which there's very little neutral hydrogen, is called the "
Lockman Hole" for its discoverer, radio astronomer Felix Lockman. The Lockman Hole provides astronomers a unique window to look beyond the Galaxy. The image above shows a survey of the Lockman Hole by the Chandra X-ray Observatory. The numerous point sources seen in this image primarily show X-ray emission from supermassive black holes. This survey, and others like it, are helping astronomers to take a full inventory of the supermassive black holes in the universe - their number, distribution and growth history. Illustrations of two types of supermassive black holes are shown above right.